The invention described herein is particularly adapted for use in a system such as that disclosed in the aforementioned Zimmerman U.S. Pat. No. 3,310,293. The system disclosed in that patent permits separate storage of dry concrete constituents or ingredients in individual tanks or compartments. The ingredients are selectively fed in predetermined proportions to a mixing trough wherein they are mixed with water to form concrete of the desired characteristic. A metering system is disclosed for the stored cement wherein a drum or metering wheel, having a plurality of radially-extending vanes, is disposed at the bottom of the cement storage bin and rotates within a chamber to deliver metered amounts of cement to a conveyor belt passing below the metering wheel.
The aforementioned U.S. patent application Ser. No. 293,182 describes a method and apparatus for removing cement from the metering wheel periphery and vanes when such cement agglomerates thereon. However, there is another cleaning problem associated with cement metering wheels. Specifically, such metering wheels, by design, have a close tolerance in mating parts. It is not uncommon to find material in the cement powder, such foreign material taking the form of steel pieces, bolts, wood, etc. These objects will not pass through the metering wheel and will cause the shear pin on the wheel drive mechanism to shear. It is therefore necessary to have access to the interior of the wheel in order to remove foreign objects. However, any aperture large enough to permit removal of an object lodged in the cement wheel is also large enough for the cement to spill out during the feed from the gravity-feed storage tank. The spillage is both wasteful and messy. Of course, one can completely disassemble the metering wheel from the storage tank after the storage tank is empty; however, this is time consuming and inconvenient in that it requires emptying of the cement storage tank.